Quirks and Quarks

How an important study of vaccine mixing in Canada got undermined by COVID chaos

An important clinical trial looking at details of safety and immune-stimulating effects of mixed doses was undermined by changing vaccine protocols and bureaucratic complexity.

Only 200 of 1,200 planned subjects were recruited

Canadian Prime Minister Justin Trudeau receives his COVID-19 vaccine booster shot at a pharmacy in Ottawa on Tuesday, Jan. 4, 2022. The Prime Minister was one of millions of Canadians who mixed vaccines. His first shot was AstraZeneca, and his second, Moderna. (Sean Kilpatrick/The Canadian Press)

Canada was one of the relatively few countries that widely adopted the practice of mixing COVID-19 vaccines. About a million and a half Canadians got a first dose of the Oxford-AstraZeneca vaccine, and a second dose of Pfizer-BioNTch or Moderna. About three million Canadians mixed Pfizer and Moderna. And as second doses and boosters have rolled out, the advice we've gotten from many doctors has been to get the vaccine that's available.

Public health authorities were confident that vaccine mixing like this was safe and effective, based on experience with many other vaccines. 

But more strong scientific evidence is always valuable when it comes to public health. That's why last February, Dr. Joanne Langley and her colleagues began a clinical trial to provide hard numbers on the safety and immune-stimulating function of different vaccine mixes. It was called the MOSAIC study, which stands for the Mix and match of the second COVID-19 vaccine dose for SAfety and Immunogenicity.

However, the rapid progress of the COVID-19 pandemic, swiftly changing vaccine protocol guidelines and the complexities of a multi-province, multi-centre study meant that they recruited only 200 of the 1,200 participants they'd planned, and were not able to accomplish all the goals of their study. They're hoping for better outcomes with MOSAIC-2, a study of mixing booster vaccines.

The story is an illustration of the difficulty of trying to study a pandemic while in the middle of it.

Click on the link above to hear Bob McDonald's interview with Joanne Langley.

Produced and written by Jim Lebans